The Fort Laramie Treaty of 1851 with the United States confirms as Crow lands a large area centered on the Big Horn Mountains: the area runs from the Big Horn Basin on the west, to the Musselshell River on the north, and east to the Powder River; it includes the Tongue River basin.
However, the Cheyenne and many bands of Lakota Sioux have been steadily migrating westward across the plains for two centuries, and are still pressing hard on the Crows.